Think Fast

People frequently ask if one is permitted to shower or bathe on the 17th of Tammuz, Asarah B’Teves, or Tzom Gedaliah. A daf learned this week by daf yomi participants may shed some light on this issue.
In ancient times, Beis Din used to convene every month to determine when the new month started. Theoretically, every month could have either 29 or 30 days, so it was necessary for Beis Din to spread the word so that everyone knew when the new month began. After determining when the new month started, they would send messengers armed with the latest calendar information to the outlying Jewish communities. (Google Calendar hadn’t been invented yet.)
The mishnah states that Beis Din sent the messengers only six times during the year: (1) in Nissan to ensure everyone knew when the correct date for Pesach was; (2) in Av for clarifying the correct day for Tishah B’Av; (3) after Rosh Chodesh Elul so that everyone knew when to start Rosh Hashanah; and in (4) Tishrei; (5) Kislev; and (6) Adar for the sake of Sukkos, Chanukah, and Purim, respectively.